The present disclosure relates to a method for the purification of bisphenol A. More particularly, the disclosure relates to an economical method and apparatus for the purification of para, para-bisphenol-A.
The compound, para, para-bisphenol A (hereinafter referred to as p,p-BPA) has been previously prepared, for example from acetone and phenol in the presence of an acid catalyst according to methods known in the art. The p,p-BPA prepared in this manner generally comprises the ortho isomer of bisphenol-A, generally referred to as ortho, para-bisphenol-A (hereinafter referred to as o,p-BPA), unreacted phenol, isopropenyl phenol (hereinafter referred to as IPP), 2,4-Bis[2-(4-hydroxyphenyl)propyl]phenol (hereinafter referred to as BPX-1), 4-[1-methyl-1-{2,2,4-trimethyl-4-(p-hydroxyphenyl)-chroman-6-yl}-ethyl]-phenol (hereinafter referred to as BPX-II), 4-(2,2,4-trimethyl-chroman-4-yl)-phenol (chroman 1.0) and 4-(2,4,4-trimethyl-chroman-2-yl)-phenol (chroman 1.5), (hereinafter collectively referred to as chromans) and dimers. The p,p-BPA prepared in this manner may be suitable, without further purification, for use as a monomer unit for the preparation of other polymers, for example, polycarbonates.
However, if the polymers prepared from bisphenol-A are to be of a particular purity, the purity of the bisphenol-A monomer would need to match these requirements. For relatively pure polymers, the purity required of p,p-BPA is generally about 99.5 to about 99.9%. Presently, to get these required purities, bisphenols obtained in the manner described above are further purified, for example, by melt crystallization of the bisphenol monomer or by adduct formation with the phenol and subsequent removal of the phenol. However, these additional purification steps are relatively costly. Alternatively, bisphenol A/phenol adducts with less than 10% isomers and phenol have been purified by fractionating under vacuum and distillation, with the successive separation of high-boiling, low-boiling, and undistilled components to provide highly pure bisphenol-A. However, as noted, successful use of this method requires a relatively pure starting material to obtain highly pure p,p-BPA, e.g., less than 10% isomers.
Thus, what is needed is a more robust method for obtaining pure p,p-BPA. Preferably, the method is economically practical and permits the use of a bisphenol feed stream from any source, such as for example, a product stream from a bisphenol-A process, impure bisphenol flakes and others.